1. Field of the Invention
The present invention relates to a wheel having a controlled pressure.
2. Description of the Related Art
A wheel for two-wheeled or four-wheeled vehicles generally comprises a rim coupled with a pneumatic tyre that is inflated to a predetermined operating pressure.
Said tyre generally comprises a carcass structure having at least one carcass ply and at least one annular reinforcing structure associated with the carcass ply, a tread band of an elastomer material at a radially external position to the carcass structure, a belt structure interposed between the carcass structure and the tread band and a pair of sidewalls located at axially opposite positions on the carcass structure.
In tubeless tyres the tyre airtightness is ensured by the radially inner layer of said carcass structure generally referred to as “liner”. In use, due for example to the natural air loss through said liner (which generally is not perfectly airtight), pressure within the tyre decreases so that the vehicle's driver is obliged to a periodical restoration of said pressure.
In an attempt to make the tyre pressure substantially constant over a rather long period of time, a solution has been suggested which contemplates use of rims internally housing a tank of gas under pressure to a higher pressure than the operating pressure of the tyre. By means of one or more valves suitably operated, pressure is restored when required.
U.S. Pat. No. 6,601,625 B2 discloses a wheel with a compressed-air tank integrated into the rim. More specifically, it is disclosed a high-pressure tank to store compressed air from an outer source, a first mechanical valve allowing the compressed air to flow from an outer source to the high-pressure tank, a second mechanical valve allowing air passage from the high-pressure tank to the inner tube of the tyre, a third valve releasing air from the inner tube of the tyre and a fourth valve releasing air from the high-pressure tank. The wheel described in said patent keeps the tyre pressure within a predetermined value in a mechanical manner, so that the necessity for the vehicle's driver to manually inflate the tyre for reaching the desired pressure is reduced. When pressure within the tyre decreases below a predetermined threshold value, the air stored in the high-pressure tank is released into the tyre so that the latter is maintained inflated to the desired minimum pressure, whereas when pressure in the tyre increases beyond a predetermined threshold value, the air is released from the tyre into the surrounding atmosphere.
U.S. Pat. No. 4,067,376 discloses a system for automatically re-admitting the air lost by a tyre during the vehicle running in order to minimise the effect of a burst. The wheel is made with an integrated annular bladder that is adapted to store an amount of compressed air under high pressure. A pressure safety valve is placed between said bladder and the tyre and is adapted to release air from the bladder to the tyre each time pressure within the tyre decreases under a predetermined limit.